1. Field of the Invention
The present invention relates to a base station apparatus and a communication method.
2. Description of the Related Art
According to a conventional mobile communication network, a hand-over processing has been carried out at each terminal as move directions of terminals are not uniform and are in various directions. In this case, hand-over processing information has been transmitted between a terminal and a base station through a radio channel that is used for control information between the terminal and the base station. A radio channel for the control information has been prescribed by, for example, the ITU-T recommendation Q.1063 Digital PLMN Channel Structures and Access Capabilities at the Radio Interface (Um Reference Point).
According to this recommendation, radio channels are broadly classified into a traffic channel (TCH) for transmitting user data by radio, and a control channel (CCH) for transmitting control information by radio. As the information transmitted during a hand-over is the control information, this control information is transmitted by radio using the latter CCH. Based on the information to be transmitted, the CCH is further divided into an associated control channel (ACCH), a dedicated control channel (DCCH), a common control channel (CCCH), a broadcast control channel (BCCH), and a user packet channel (UPCH). Applications of these control channels will not be particularly explained here.
Next, according to Personal Handy Phone System ARIB Standard Version 3, RCR STD-28, issued by the ARIB (the Association of Radio Industries and Businesses), it is described that the control information for the hand-over processing is transmitted by radio using the ACCH. The ACCH is further divided Into a slow associated control channel (SACCH), and a fast associated control channel (FACCH). The control information for the hand-over processing is transmitted by radio using the SACCH.
As an example of a hand-over processing carried out at each terminal according to the prior-art technique, a hand-over processing in a personal handy phone system (PHS) is described in Personal Handy Phone System ARIB Standard Version 3, RCR STD-28 (the second generation cordless telephone system standards, Version 3, Fascicle 1), issued by the ARIB (the Association of Radio Industries and Businesses). According to the conventional mobile communication network, where there are various directions in the move of terminals, hand-over destinations and hand-over executing timings are different between the terminals. As a result, according to the conventional technique, each terminal executes the hand-over processing.
FIG. 1 shows an outline of the hand-over processing described in Personal Handy Phone System ARIB Standard Version 3, RCR STD-28 (the second generation cordless telephone system standards, Version 3, Fascicle 1), issued by the ARIB (the Association of Radio Industries and Businesses).
When a certain mobile station (corresponding to a terminal in embodiments to be described later) 600 is going to move from a service area that is managed by a certain base station (corresponding to a fixed base station in the embodiments to be described later) 700 to another service area managed by the same base station 700, the mobile station 600 transmits a link channel establishment request 800 to this base station 700. Upon receiving this link channel establishment request 800, the base station 700 allocates a radio link channel of a hand-over destination to this mobile station 600, and notifies a result of this allocation to this base station 700 as a link channel allocation 810.
When this radio link channel of a hand-over destination has been allocated to the mobile station 600, the mobile station 600 transmits a call setup 820 to the base station 700. Upon receiving the call setup 820, the base station 700 carries out a call connection processing at the hand-over destination.
In the case of accepting a call corresponding to the call setup 820, the base station 700 posts a call setup acceptance 830 to the mobile station 600. In response to this call setup acceptance 830, the mobile station 600 that has finished the call setup processing notifies an authentication request 840 to the base station 700. The base station 700 confirms whether this mobile station 600 is a correct mobile station or not, based on the authentication request 840. The base station 700 then notifies a result of this authentication to the mobile station 600 as an authentication response 850.
The mobile station 600 that has been authenticated as shown in the authentication response 850 by the base station 700 notifies a radio channel disconnection 860 to the base station 700 in order to disconnect the link before the hand-over. The base station 700 that has received the radio channel disconnection 860 releases the setting of this mobile station 600 before the hand-over, and notifies this effect to the mobile station 600 as a radio channel disconnection completion 870.
As explained above, according to the existing mobile communication system, a hand-over processing is carried out for each terminal 600.
In actual practice, there is considered a case where many terminals move in the same direction at the same time. For example, there is a case where passengers on a train or on an airplane are carrying out communications using their mobile terminals. When a plurality of terminals within a service area of a certain base station have moved to the same direction together, the plurality of terminals start a hand-over processing using respective SACCHs. As a result, the control information between the terminal, the base station and the exchange increases rapidly because of the hand-over processing. This has had a problem that the load of the network becomes high.
According to the existing mobile communication system (including a PHS system shown in the embodiments of the present invention to be described later), various control information has been necessary in addition to the user data. The control information is classified into a plurality of types based on the kinds of the control information. Radio channels for transmitting data are allocated on that classification basis. In other words, as described above, the CCH through which the control information is transmitted includes the ACCH, DCCH, CCCH, BCCH, and UPCH that are allocated to the plurality of corresponding kinds of control information. The transmission of the control information at the time of the hand-over processing is carried out using the SACCH out of the SACCH and the FACCH that are the sub-divisions of the ACCH.
In the radio communication, the transmission band is limited as compared with that or the wire communication. Therefore, there has been a particularly high demand for the effective utilization of the transmission band for the radio communication. The allocation of a separate radio channel to each kind of the control information with one classified channel (each of the above-described plurality of kinds of channels) used as one unit does not contribute to the effective utilization of the transmission band.
According to Japanese Patent Application Laid-open Publication No. Hei 9-121188, the following mobile communication system (prior-art technique 1) has been disclosed. According to the prior-art technique 1, in the mobile communication system that cannot manage the hand-over processing during a high-speed moving like the PHS, a mobile base station and a relay station are installed within a high-speed moving unit for providing a communication service during a high-speed moving. A PHS terminal is connected to an ISDN through the mobile base station, the relay station, a base station and an exchange.
According to the existing mobile communication system (including the PHS), the radio channels for the control information exist as described above. Therefore, in order to effectively utilize the limited radio transmission band (the radio channels), a further ingenuity is required.
According to Japanese Patent Application Laid-open Publication No. Hei 11-234736, the following mobile communication system (prior-art technique 2) has been disclosed. The prior-art technique 2 consists of an existing base station for managing a fixed radio control zone covering a predetermined area, a mobile base station for managing a moving radio control zone that has been allocated to an internal space of a moving vehicle, and a mobile station. The mobile base station has first communication means for carrying out a communication processing as a mobile station between the mobile base station and the existing base station, second communication means for carrying out a communication processing as a base station between the mobile base station and the mobile station within the moving radio control zone, and mobile base station control means for carrying out a connection control of a path between the first communication means and the second communication means. The first communication means has a plurality of control channels between the mobile base station and the existing base station, and sequentially carries out a perch scanning starting from a control channel that has become unused.
According to the prior-art technique 2, a plurality of control channels are used (allocated) in a limited radio transmission band (radio channels). Therefore, it is not possible to effectively utilize the radio transmission band (the radio channels).
According to Japanese Patent Application Laid-open Publication No. Hei 9-84126, the following mobile communication system (prior-art technique 3) has been disclosed. The prior-art technique 3 comprises a plurality of base stations, each being connected to a public communication network via a wired channel and forming one of a group of first cells of a predetermined size along a moving path of a high-speed moving vehicle, at least one relay station that forms on the high-speed moving vehicle a second cell being smaller than the first cell, and a moving unit that can move at a low speed on the high-speed moving vehicle. The relay station and the moving unit have a first radio interface for connecting between the moving unit and the relay station via a first radio channel during a communication of the moving unit. The base stations and the relay station have a second radio interface for connecting between the base stations and the relay station via a second radio channel cooperatively with the connection operation of the first radio interface via the first radio channel, and for connecting this second radio channel with the first radio channel, and base station hand-over means for switching over between the base stations that become connection destinations of the relay station while holding the first radio channel when the high-speed moving vehicle moves between the first cells.
The relay station has a relay transceiver exclusively used for the control channels, and a separate relay transceiver exclusively used for the communication channels.
According to the prior-art technique 3, there are radio channels exclusively used for the control channels. Therefore, it is not possible to effectively utilize the radio transmission band (the radio channels) by this portion.
According to Japanese Patent Application Laid-open Publication No. Hei 6-244780, the following mobile communication method (prior-art technique 4) has been disclosed. The prior-art technique 4 has a mobile radio communication system comprising a plurality of base stations, a large number of mobile stations that can be connected to these base stations via radio channels, and a control station for controlling the plurality of base stations. The control station has memory means for registering, for each mobile station, one or more base stations that should page the mobile station, means for updating the registered contents of the memory means as the mobile stations move, and means for controlling so that the paging of the mobile stations is executed by the base stations registered in the memory means. In this mobile radio communication system, means for relay connecting between the mobile stations and the control station via the base stations is mounted on a moving vehicle. The mobile stations have means for connecting to the relay connecting means. The relay connecting means has means for registering the mobile stations connected by the means for connecting, means for notifying subscriber numbers of the registered mobile stations and position information of the relay connecting means to the control station via the base stations, and means for relay connecting the connection control and communication of the registered mobile stations.
The means for connecting has means for connecting by using relay control channels different from the control channels of the base stations.
According to the prior-art technique 4, in addition to the control channels, there are the relay control channels. Therefore, it is not possible to effectively utilize the radio transmission band (the radio channels) by this portion.
Therefore, it has been required to decrease the volume of control information during the hand-over processing. Further, it has been required to effectively utilize the limited radio transmission band (the radio channels).